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Date: Wed, 22 Jun 2022 11:31:21 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: corbet@....net, david@...hat.com, mike.kravetz@...cle.com,
osalvador@...e.de, paulmck@...nel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
duanxiongchun@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v5 0/2] make hugetlb_optimize_vmemmap compatible with
memmap_on_memory
On Tue, Jun 21, 2022 at 01:53:13PM -0700, Andrew Morton wrote:
> On Mon, 20 Jun 2022 19:06:14 +0800 Muchun Song <songmuchun@...edance.com> wrote:
>
> > This series makes hugetlb_optimize_vmemmap compatible with memmap_on_memory
> > and is based on mm-stable. The reason refers to the patch 2's commit log.
> >
> > v5:
> > - Replace enum to defines per David.
> > - Walk vmemmap page tables to avoid false-positive.
>
> I can't see this second change in the v3->v5 deltas?
>
My changlog is not clear, Let me clarify it here.
v3: Drop a section flag SECTION_CANNOT_OPTIMIZE_VMEMMAP and introduce a page
flag PageVmemmapSelfHosted to make both parameters compatible.
v4: Fix compiling error when !CONFIG_MEMORY_HOTPLUG and a bug when memory block
spans multiple sections.
v5: Fix a bug which PageVmemmapSelfHosted() check can be false-positive.
Thanks.
> From: Muchun Song <songmuchun@...edance.com>
> Subject: mm-memory_hotplug-enumerate-all-supported-section-flags-v5
> Date: Mon, 20 Jun 2022 19:06:15 +0800
>
> replace enum with defines per David
>
> Link: https://lkml.kernel.org/r/20220620110616.12056-2-songmuchun@bytedance.com
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>
> include/linux/mmzone.h | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> --- a/include/linux/mmzone.h~mm-memory_hotplug-enumerate-all-supported-section-flags-v5
> +++ a/include/linux/mmzone.h
> @@ -1439,16 +1439,13 @@ enum {
> SECTION_MAP_LAST_BIT,
> };
>
> -enum {
> - SECTION_MARKED_PRESENT = BIT(SECTION_MARKED_PRESENT_BIT),
> - SECTION_HAS_MEM_MAP = BIT(SECTION_HAS_MEM_MAP_BIT),
> - SECTION_IS_ONLINE = BIT(SECTION_IS_ONLINE_BIT),
> - SECTION_IS_EARLY = BIT(SECTION_IS_EARLY_BIT),
> +#define SECTION_MARKED_PRESENT BIT(SECTION_MARKED_PRESENT_BIT)
> +#define SECTION_HAS_MEM_MAP BIT(SECTION_HAS_MEM_MAP_BIT)
> +#define SECTION_IS_ONLINE BIT(SECTION_IS_ONLINE_BIT)
> +#define SECTION_IS_EARLY BIT(SECTION_IS_EARLY_BIT)
> #ifdef CONFIG_ZONE_DEVICE
> - SECTION_TAINT_ZONE_DEVICE = BIT(SECTION_TAINT_ZONE_DEVICE_BIT),
> +#define SECTION_TAINT_ZONE_DEVICE BIT(SECTION_TAINT_ZONE_DEVICE_BIT)
> #endif
> -};
> -
> #define SECTION_MAP_MASK (~(BIT(SECTION_MAP_LAST_BIT) - 1))
> #define SECTION_NID_SHIFT SECTION_MAP_LAST_BIT
>
> _
>
>
>
>
> From: Muchun Song <songmuchun@...edance.com>
> Subject: mm-memory_hotplug-make-hugetlb_optimize_vmemmap-compatible-with-memmap_on_memory-v5
> Date: Mon, 20 Jun 2022 19:06:16 +0800
>
> walk vmemmap page tables to avoid false-positive
>
> Link: https://lkml.kernel.org/r/20220620110616.12056-3-songmuchun@bytedance.com
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Co-developed-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
>
> mm/hugetlb_vmemmap.c | 69 ++++++++++++++++++++++++++---------------
> 1 file changed, 44 insertions(+), 25 deletions(-)
>
> --- a/mm/hugetlb_vmemmap.c~mm-memory_hotplug-make-hugetlb_optimize_vmemmap-compatible-with-memmap_on_memory-v5
> +++ a/mm/hugetlb_vmemmap.c
> @@ -10,6 +10,7 @@
> */
> #define pr_fmt(fmt) "HugeTLB: " fmt
>
> +#include <linux/memory.h>
> #include "hugetlb_vmemmap.h"
>
> /*
> @@ -99,34 +100,52 @@ int hugetlb_vmemmap_alloc(struct hstate
> static unsigned int vmemmap_optimizable_pages(struct hstate *h,
> struct page *head)
> {
> - struct mem_section *ms;
> - struct page *vmemmap_page;
> - unsigned long pfn = page_to_pfn(head);
> -
> if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
> return 0;
>
> - ms = __pfn_to_section(pfn);
> - vmemmap_page = sparse_decode_mem_map(ms->section_mem_map,
> - pfn_to_section_nr(pfn));
> - /*
> - * Only the vmemmap pages' vmemmap may be marked as VmemmapSelfHosted.
> - *
> - * Due to HugeTLB alignment requirements, and the vmemmap pages being
> - * at the start of the hotplugged memory region. Checking any vmemmap
> - * page's vmemmap is fine.
> - *
> - * [ hotplugged memory ]
> - * [ vmemmap ][ usable memory ]
> - * ^ | | |
> - * +---+ | |
> - * ^ | |
> - * +--------+ |
> - * ^ |
> - * +-----------------+
> - */
> - if (PageVmemmapSelfHosted(vmemmap_page))
> - return 0;
> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
> + pmd_t *pmdp, pmd;
> + struct page *vmemmap_page;
> + unsigned long vaddr = (unsigned long)head;
> +
> + /*
> + * Only the vmemmap page's vmemmap page can be self-hosted.
> + * Walking the page tables to find the backing page of the
> + * vmemmap page.
> + */
> + pmdp = pmd_off_k(vaddr);
> + /*
> + * The READ_ONCE() is used to stabilize *pmdp in a register or
> + * on the stack so that it will stop changing under the code.
> + * The only concurrent operation where it can be changed is
> + * split_vmemmap_huge_pmd() (*pmdp will be stable after this
> + * operation).
> + */
> + pmd = READ_ONCE(*pmdp);
> + if (pmd_leaf(pmd))
> + vmemmap_page = pmd_page(pmd) + pte_index(vaddr);
> + else
> + vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr));
> + /*
> + * Due to HugeTLB alignment requirements and the vmemmap pages
> + * being at the start of the hotplugged memory region in
> + * memory_hotplug.memmap_on_memory case. Checking any vmemmap
> + * page's vmemmap page if it is marked as VmemmapSelfHosted is
> + * sufficient.
> + *
> + * [ hotplugged memory ]
> + * [ section ][...][ section ]
> + * [ vmemmap ][ usable memory ]
> + * ^ | | |
> + * +---+ | |
> + * ^ | |
> + * +-------+ |
> + * ^ |
> + * +-------------------------------------------+
> + */
> + if (PageVmemmapSelfHosted(vmemmap_page))
> + return 0;
> + }
>
> return hugetlb_optimize_vmemmap_pages(h);
> }
> _
>
>
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